I noticed in the parts manual three different styles of cross-over fuel line between the tanks for my 1958 panhead. What was the purpose of the "loop de loop" version (full loop in the middle) versus a semi-straight run between the tanks? Was it for cosmetics or did it serve a purpose?

I am going to venture a guess that it has the loop to help keep tension from the nipples.
It would help with metal fatigue, fitment, and expansion/contraction.
That is the way I handle a lot of my metal line installations.
Just a guess though.
Dale